Figure. Serratia marcescens facilitates arboviruses to infect Aedes mosquitoes via secretion of SmEnhancin

       With the support of the National Natural Science Foundation of China (Grant No. 81730063, 81571975, 81420108024), the research team of Professor Gong Cheng at Tsinghua University in cooperation with Southern Medical University made an important progress in mosquito-arbovirus interactions. They identified a gut commensal bacterium, Serratia marcescens, that facilitates arboviruses to infect Aedes mosquitoes via secreting a bacteria effector SmEnhancin. The relevant research results were published in Cell Host & Microbe on December 27, 2018, titled "A Gut Commensal Bacterium Promotes Mosquito Permissiveness to Arboviruses". The weblink is: https://www.cell.com/cell-host-microbe/fulltext/S1931-3128(18)30561-4。

Mosquitoes are hematophagous vectors for hundreds of human pathogens such as dengue virus, Zika virus and West Nile virus. The midgut, which harbors abundant commensal microbes, is the first and pivotal virus entry site that determines mosquito vector competence. However, how the individual microbe regulates the arboviral transmission by mosquitoes remains unexplored.

In this study, Dr. Cheng and his colleagues isolated 21 cultivable bacteria species from the Aedes aegypti midgut, evaluated their respective effect to arbovirus infection, and identified that S. marcescens significantly enhanced arboviruses to infect the Aedes mosquitoes. They also found that field Aedes mosquitoes with the gut residency of S. marcescens were more permissive to DENV infection than those free of S. marcescens. Oral introduction of S. marcescens into field mosquitoes that lack this bacterium rendered these mosquitoes highly susceptible to arboviruses. They revealed that S. marcescens facilitated arboviral infection through a secreted protein named SmEnhancin, which digested membrane-bound mucins on the mosquito gut epithelia and enhanced viral dissemination across the gut barrier.

This study identifies S. marcescens as an important indicator to dengue prevalence, and reveals the multipartite interactions among hosts, the gut microbiome and viruses. The study elucidates the mechanism of S. marcescens facilitating arbovirus infection, providing prospective strategies against viral infection and transmission.